Multi-resolution haptic interaction of hybrid virtual environments

This sheet deals with analysis of the oblique impact system, which is composed of the golf-ball and club. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of ball. The characteristics of the oblique impact were obtained by using this model. In previous studies,the validity of the normal model was confirmed, validity of tangential model was not confiemed. Therefore, reconsider the tangential model. The result is improved accuracy of the model. Also.examined the characteristics of oblique impacts of changes in coefficient of friction from experiments and analysis.

This sheet deals with characteristics of the oblique impact system, which is composed of the ball and flat surface. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of ball. The characteristics of the oblique impact were obtained by using this model. The results show that the spin rate increased in proportion to the angle of incidence and impact velocity. Also, in the case of increase the tangential stiffness, the spin rate was decreased and the angel of reflection was increased.

Problems connected with a shock interaction of a thin elastic cylindrical bar and an elastic sphere with an Uflyand-Mindlin plate of a finite size are considered. In enumerated problems, an impact process is accompanied by material local deformations and propagation of wave surfaces of a strong or weak discontinuity in elastic bodies coming in contact. The local deformations are taken into account in terms of the Hertz's contact theory, but the dynamic deformations behind the fronts of incident and reflected waves are determined by means of truncated power series with variable coefficients (what is known as ray series). These two types of deformations are mated on the contact region boundary. As the truncated ray series, as a rule, are not uniformly applicable in the whole region of the wave solution existence, then for their improvement the method of “forward-area” regularization is used which is based on a combination of the recurrent equations of the ray method with the method of multiple scales. The method of power series (ray method) allows one to find the main characteristics of the impact theory in an analytical form.

The ball-on-ring (BOR) test is an effective technique used to characterize the biaxial fracture strength of brittle materials. In particular, damages induced by wafer backgrinding process can be evaluated using the BOR test. It is difficult to measure directly the radius of contact area between the loading ball and a specimen, which is needed for stress determination by an analytic solution. In this study, parametric finite element analyses were performed to compare with known closed-form solutions. It was found that the effect of small loading area must not be ignored and that the radius of contact could be precisely determined using Hertz's contact theory. This can serve as a guideline to accurately obtain the fracture strength of a BOR specimen.

In this paper, photoelastic experimental hybrid method using external traction free boundary condition and using the relative equation of two stress functions in contact problems are developed. Their validities are confirmed through experiments and discussions Hertz's contact theory and two photoelastic experimental hybrid methods explained above are applied to the stress analysis of O-ring under 10% or 20% squeeze rate. Among them, the photoelastic experimental hybrid method using the relative equation of two stress functions in contact problems is most effective. When squeeze rates of O-ring are 20%, Maximum of absolute σ_x is greater than maximum of absolute σ_y by little. But they are almost equal to each other. Maximums of absolute τ_<xy> are 1/5 of absolute σ_x when squeeze rate of O-ring is 20%.

An effective method for calculating elasto-plastic contact pressure and contact patch size under elliptical, circular and line contact conditions

In industrial plants and pressurized equipment, leakage control and prevention are key tasks in preventive maintenance programs. The most critical element in these types of equipment is the seals. Several types of seals are used and the most popular are flat seals and O-rings. Two conditions affect the proper functioning of the seals: the mounting configuration and the initial loading parameters during operation. In this work, the analysis of the mechanical and leakage behaviour of the O-ring seal, when installed either in a cylindrical concave groove or in a rectangular one, is presented. Two finite element models were developed with Ansys software to study the behaviour of the assemblies in both cases when the clamping load is applied and when the assembly is pressurized. The results of the numerical models are compared to the analytical approach based on Hertz's contact theory. This study shows that the use of a cylindrical concave groove for mounting elastomeric O-rings can improve sealing in pressurized systems.

This sheet deals with characteristics of the oblique impact system, which is composed of the golf ball and elastic supported clubface. The impact system is modeled by both a nonlinear spring and a nonlinear dashpot using Hertz's contact theory. This model is applied to the oblique impact system of golf ball and elastic supported clubface. The characteristics of the oblique impact were obtained by using this model. The results show that the spin rate increased in proportion to the angle of incidence and impact velocity and a coefficient of friction. Also, in the case of increase the tangential stiffness, the spin rate was decreased.

We report on the results of extensive computer simulation of the effect of deformation on the morphology of a porous medium and its fluid flow properties. The porous medium is represented by packings of spherical particles. Both random and regular as well as dense and nondense packings are used. A quasistatic model based on Hertz's contact theory is used to model the mechanical deformation of the packings, while the evolution of the permeability with the deformation is computed by the lattice-Boltzmann approach. The evolution of the pore-size and pore-length distributions, the porosity, the particles' contacts, the permeability, and the distribution of the stresses that the fluid exerts in the pore space are all studied in detail. The distribution of the pores' lengths, the porosity, and the particles' connectivity change strongly with the application of an external strain to the porous media, whereas the pore-size distribution is not affected as strongly. The permeability of the porous media strongly reduces even when the applied strain is small. When the permeabilities and porosities of the random packings are normalized with respect to their predeformation values, they all collapse onto a single curve, independent of the particle-size distribution. The porosity reduces as a power law with the external strain. The fluid stresses in the pore space follow roughly a log-normal distribution, both before and after deformation.

The vocal folds are subject to repeated collision during phonation. The resulting contact pressure is often considered to play an important role in vocal fold injury, and has been measured in many experimental studies. In this study, vocal fold contact pattern and contact pressure during phonation were numerically investigated and compared to Hertzian contact theory. The results show that vocal fold contact in general occurs within a horizontal strip on medial surface, first appearing at the inferior medial surface and propagating upward. Because of the localized and traveling nature of vocal fold contact, sensors of a finite size may significantly underestimate the peak vocal fold contact pressure (by about as large as 80% for a sensor diameter of 2 mm), particularly for vocal folds of low transverse stiffness or thick medial surface. In general, the contact pressure increases with the size and curvature of the contact area, as predicted from Hertzian contact theory, indicating the possibility of estimating vocal fold contact pressure from medial surface kinematics. However, deviations from Hertzian theory were also observed, which need to be taken into consideration in estimating vocal fold contact pressure.

Ultra-high molecular weight polyethylene (UHMWPE) was modified on purpose to enhance the wear resistance. The modification was done either by crosslinking the amorphous region of the surface using difunctional monomers or by crosslinking the bulk in the melt state using peroxide. The changes in thermal and tensile properties indicated that the modifications were effected. The volumetric wear rate, determined on a pin-on-disk wear tester, was suppressed by the modifications. The correlation between the tensile properties and the wear rates was sought. Any single tensile property or tensile rupture energy did not correlate well with the observed wear rate. Instead, the ratio of maximum contact stress calculated by the Hertz's contact theory to yield stress appeared to correlate well with volumetric wear rate.

Haptic interaction in slow virtual environments (VEs) can become unstable due to the phase lag introduced in the control loop by the slow update rate of the VE. Increasing the physical damping and/or limiting the contact stiffness rendered to users can mitigate the destabilizing effect of the low VE update rate. However, large physical damping and compliant virtual contacts decrease the sense of presence in VEs, especially during interaction with rigid virtual objects. To increase the maximum virtual contact stiffness that can be rendered to users without increasing the interface damping, this paper proposes a control strategy based on multirate wave communications between a haptic interface and a VE updated at a slow and fixed rate. The multirate wave communications are shown to be guaranteed passive only if the decrease of the wave sampling rate at the connection between the haptic interface and the VE does not cause aliasing. Therefore, an antialiasing low-pass filter is placed before the wave rate drop in the communications. The passivity condition is verified analytically and numerically for multirate haptic interaction in VEs with various contact stiffnesses and update rates. The transparency of haptic interaction in slow VEs to which users connect via passive multirate wave communications is investigated analytically in the frequency domain. Experiments validate that passive multirate wave communications can render stiffer contact in slow VEs than conventional direct coupling, and illustrate the destabilizing effect of the aliasing caused by the sampling rate drop in the communications.

Often, designers and developers of serious games (and virtual simulations in general) strive for high fidelity (realism). However, real-time high-fidelity rendering of complex environments across sensory modalities such as vision, audition, and haptic (sense of touch) is still beyond our computational reach. Previous work has demonstrated that multimodal effects can be considerable, to the extent that a large amount of detail of one sense may be ignored or enhanced by the presence of other sensory inputs. Taking advantage of such multimodal effects, perceptual-based rendering—whereby the rendering parameters are adjusted based on the perceptual system—can be employed to limit computational processing. Motivated by the general lack of emphasis given to the understanding of audio rendering in virtual environments and games, we have started investigating multimodal (audiovisual) interactions within such virtual environments. Our work has shown that sound can directly affect visual fidelity perception and task performance within a virtual environment. These effects can be very individualized, whereby the influence of sound is dependent on various individual factors including musical listening preferences, suggesting the importance of individualizing the virtual environment to each user. This chapter begins with an overview of virtual environments and serious gaming’s open problems, with an emphasis on fidelity, and multimodal interactions, and the implications that these may have on performance and computational requirements. A detailed summary of our own prior work will be provided along with insight and suggestions that may guide designers and developers of serious games and virtual learning environments in general. Although the chapter is contextualized in the use of serious games in health professions education, the information provided is generalizable across a variety of domains.

Haptic rendering has the potential to increase the quality of human-computer interaction with virtual environment by accommodating the sense of touch. In this paper, a 7 DOF arm type exoskeleton device is designed and implemented. Human user can haptically interact with virtual environment by using this light-weight device. The principles of measuring user's arm motions are presented, which include the dimensional mechanism. The motion of each joint of the proposed haptic device is nearly independent. The virtual contact force is also calculated in real time to meet the stringent requirement of real time haptic rendering. Experiments results show promising feasibility of the arm type exoskeleton device.

For determining die strength, there are a couple of tests available in the literature, such as three-point and four-point bending, ball breaker, ball-on-the-ring, ring-on-the-ring, and recently proposed ball-on-elastic- pad (BoEP) and ball-on-the-hole (BoH) tests. It's well known that the test data reduction with theoretical formulations is more convenient and useful than that with numerical simulation results. However, those theoretical formulations have to be validated either by numerical simulation or experiments, before their applications. The objective of this study is to reevaluate and thus improve the existing BoEP and BoH tests for die strength using Hertzian contact theory, plate theories and finite element method (FEM). In this paper, the FEM analysis with ¿contact element¿ successfully has been verified with Hertzian contact theory and further proved that Hertzian contact theory can be employed to estimate the contact area for calculating die strength in both methods. The results indicate that the consistency between the theoretical formulation and FEM simulation for both tests exist only at the relatively large radius of ball and high applied loading, because the feasibility of the theoretical formulations requires large contact radius(> 0.06 mm) or area. For the BoEP test, the elastic moduli of elastic pad and ball have no obvious effect on the difference of maximum die stress between theoretical and FEM results. The theoretical solutions associated with contact radius determined by Hertzian contact theory are successfully proved for improving BoEP and BoH tests for die strength determination, and for better accuracy of die strength the ball with radius ranging from 2 mm to 4 mm is suggested.